[FLINK-28439][table][python] Support SUBSTR and REGEXP built-in function in Table API

[a49a]

What is the purpose of the change

Support instr and locate built-in functions in Table API.

Brief change log

• Support SUBSTR and REGEXP built-in functions in Table API.
• Support SUBSTR and REGEXP built-in functions in Python Table API.

Verifying this change

This change added tests and can be verified as follows:

• Added test that validates that SUBSTR and REGEXP in Table API work
• Added test that validates that SUBSTR and REGEXP in Python Table API work

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (yes)
• If yes, how is the feature documented? (docs)

[flinkbot]

CI report:

• dab2b1b Azure: SUCCESS

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